I think you would have to have a way to keep the wad from collapsing upon itself from the gas pressure pushing the wad in on itself.
Perhaps adding an object or objects(larger steel ball[s]) in the center of the "rose petal" and pre-fragmenting the petals. The ball(s) would push into the petal thus keeping the petals from turning inwards. The perforated or pre-fragmented petals would allow the center ball(s) to keep the pattern from ending up doughnut shaped.